Causes

In ALS, the nerve cells that control the movement of your muscles gradually die, so your muscles progressively weaken and begin to waste away.

ALS is inherited in 5 to 10 percent of cases. The other cases appear to occur randomly.

Researchers are studying several possible causes of ALS, including:

Gene mutation. Various genetic mutations can lead to inherited ALS, which appears nearly identical to the noninherited form.

Chemical imbalance. People with ALS generally have higher than normal levels of glutamate, a chemical messenger in the brain, around the nerve cells in their spinal fluid. Too much glutamate is known to be toxic to some nerve cells.

Disorganized immune response. Sometimes a person's immune system begins attacking some of his or her body's own normal cells, which may lead to the death of nerve cells.

Protein mishandling. Mishandled proteins within the nerve cells may lead to a gradual accumulation of abnormal forms of these proteins in the cells, eventually causing the nerve cells to die.

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